catfish,
Your point well taken re: headphones as reference. After all, if the Senn's give you a good sound, you should aim toward it by all means. It is just that, if you ever wish to aim at an "accurate" sound reproduction, your ultimate reference for the harpsichord sound should be the sound of live instrument, not the sound reproduced through the headphones.
I have to emphasize here that the sonic details/clarity and imaging/soundstaging are heavily interrelated to each other in stereo listening. Years ago, I had to place my Hales speakers temporarily in a less-than-optimal locations/geometry. Like in your case, L/R channel distance was much shorter than the listening distance. During that period, the Hales really sounded mediocre -- not only they didn't image properly, but all the musical details were gone. They sounded "muted" and "veiled," regardless of the small placement tweaks I tried. Simply unenjoyable. In the end, the only solution was to return the Hales to the original room placement. All the sudden, the music regained the pristine details, clarity and immediacy...
